4 Replies Latest reply on May 7, 2019 9:51 AM by RoTh_1771981

    Question about CYW920719EVB 32.768KHz Crystal

    RoTh_1771981

      We used the crystal specs mentioned in the datasheet for the 920719. 

      Parameter Symbol Conditions Minimum Typical Maximum Unit
      Output frequency Foscout 32.768 kHz
      Frequency tolerance Crystal-dependent 100 ppm
      Start-up time Tstartup 500 ms
      XTAL drive level Pdrv For crystal selection 0.5 μW
      XTAL series resistance Rseries For crystal selection 70 kΩ
      XTAL shunt capacitance Cshunt For crystal selection 2.2 pF
      External AC Input Amplitude VIN (AC) Ccouple = 100 pF;
      R
      bias= 10 Mohm
      400 mVpp

       

      We actually used a 20 PPM industrial temp grade XTL and the frequency turned out 60ppm to the high side.  By increasing the caps which didn't meet the XTL specs, I got it on frequency but now the startup time is about 1.5secs.  I even tried removing the 10MΩ feedback resistor which sped it up some since this increased gain but this isn't right.  I am sampling lower ESR XTLs now.  

       

      Can someone tell me what the part number is for the  32.768KHz XTL used on the EVB? The markings on the part don't help.  The EVB came with a schematic but no BOM.

       

      Thanks,

      Rex